Note the difference between left ventricular peak pressure and aortic peak pressure, which represents the left ventricular outflow tract gradient, has been reduced from 80 mm Hg to 9 mm
Trang 1Heart block is a frequent acute complication, so a temporary
pacing electrode is inserted via the femoral vein beforehand
and is usually left in situ for 24 hours after the procedure,
during which time the patient is monitored
The main procedural complications are persistent heart
block requiring a permanent pacemaker (10%), coronary artery
dissection and infarction requiring immediate coronary artery
bypass grafting (2%), and death (1-2%) The procedural
mortality and morbidity is similar to that for surgical myectomy,
as is the reduction in left ventricular outflow tract gradient
Surgery and ethanol septal ablation have not as yet been
directly compared in randomised studies
Septal defect closure
Atrial septal defects
Atrial septal defects are congenital abnormalities characterised
by a structural deficiency of the atrial septum and account for
about 10% of all congenital cardiac disease The commonest
atrial septal defects affect the ostium secundum (in the fossa
ovalis), and most are suitable for transcatheter closure Although
atrial septal defects may be closed in childhood, they are the
commonest form of congenital heart disease to become
apparent in adulthood
Diagnosis is usually confirmed by echocardiography,
allowing visualisation of the anatomy of the defect and Doppler
estimation of the shunt size The physiological importance of
the defect depends on the duration and size of the shunt, as well
as the response of the pulmonary vascular bed Patients with
significant shunts (defined as a ratio of pulmonary blood flow to
systemic blood flow > 1.5) should be considered for closure
when the diagnosis is made in later life because the defect
reduces survival in adults who develop progressive pulmonary
hypertension They may also develop atrial tachyarrhythmias,
which commonly precipitate heart failure
Patients within certain parameters can be selected for
transcatheter closure with a septal occluder In those who are
unsuitable for the procedure, surgical closure may be considered
Patent foramen ovale
A patent foramen ovale is a persistent flap-like opening
between the atrial septum primum and secundum which occurs
in roughly 25% of adults With microbubbles injected into a
peripheral vein during echocardiography, a patent foramen
ovale can be demonstrated by the patient performing and
Simultaneous aortic and left ventricular pressure waves before (left) and after (right) successful ethanol septal ablation Note the difference
between left ventricular peak pressure and aortic peak pressure, which represents the left ventricular outflow tract gradient, has been
reduced from 80 mm Hg to 9 mm Hg
Indications and contraindications for percutaneous closure
of atrial septal defects Indications
Clinical
x If defect causes symptoms
x Associated cerebrovascular embolic event
x Divers with neurological decompression sickness
Anatomical
x Defects within fossa ovalis (or patent foramen ovale)
x Defects with stretched diameter < 38 mm
Contraindications
x Sinus venosus defects
x Ostium primum defects
x Pulmonary:systemic flow ratio
> 1.5 and reversible pulmonary hypertension
x Right-to-left atrial shunt and hypoxaemia
x Presence of > 4 mm rim of tissue surrounding defect
x Ostium secundum defects with other important congenital heart defects requiring surgical correction
Deployment sequence of the Amplatzer septal occluder for closing an atrial septal defect
Micrograph of hypertrophied myocytes in haphazard alignments characteristic of hypertrophic
cardiomyopathy Interstitial collagen is also increased
Trang 2releasing a prolonged Valsalva manoeuvre Visualisation of
microbubbles crossing into the left atrium reveals a right-to-left
shunt mediated by transient reversal of the interatrial pressure
gradient
Although a patent foramen ovale (or an atrial septal
aneurysm) has no clinical importance in otherwise healthy
adults, it may cause paradoxical embolism in patients with
cryptogenic transient ischaemic attack or stroke (up to half of
whom have a patent foramen ovale), decompression illness in
divers, and right-to-left shunting in patients with right
ventricular infarction or severe pulmonary hypertension
Patients with patent foramen ovale and paradoxical embolism
have an approximate 3.5% yearly risk of recurrent
cerebrovascular events
Secondary preventive strategies are drug treatment (aspirin,
clopidogrel, or warfarin), surgery, or percutaneous closure using
a dedicated occluding device A lack of randomised clinical
trials directly comparing these options means optimal
treatment remains uncertain However, percutaneous closure
offers a less invasive alternative to traditional surgery and allows
patients to avoid potential side effects associated with
anticoagulants and interactions with other drugs In addition,
divers taking anticoagulants may experience haemorrhage in
the ear, sinus, or lung from barotrauma
Congenital ventricular septal defects
Untreated congenital ventricular septal defects that require
intervention are rare in adults Recently, there has been interest
in percutaneous device closure of ventricular septal defects
acquired as a complication of acute myocardial infarction
However, more experience is necessary to assess the role of this
procedure as a primary closure technique or as a bridge to
subsequent surgery
The picture of a stenotic mitral valve and micrograph of myocytes showing
hypertrophic cardiomyopathy were provided by C Littman, consultant
histopathologist at the Health Sciences Centre, Winnipeg, Manitoba,
Canada The postmortem picture of a heart with hypertrophic
cardiomyopathy was provided by T Balachandra, chief medical examiner for
the Province of Manitoba, Winnipeg The pictures of Amplatzer occluder
devices were provided by AGA Medical Corporation, Minnesota, USA.
Amplatzer occluder devices for patent foramen ovale (left) and muscular ventricular septal defects (right)
Further reading
x Inoue K, Lau K-W, Hung J-S Percutaneous transvenous mitral
commissurotomy In: Grech ED, Ramsdale DR, eds Practical
interventional cardiology 2nd ed London: Martin Dunitz, 2002:
373{87
x Bonow RO, Carabello B, de Leon AC, Edmunds LH Jr, Fedderly
BJ, Freed MD, et al ACC/AHA guidelines for the management of patients with valvular heart disease: A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Committee on Management of Patients with
Valvular Heart Disease) J Am Coll Cardiol 1998;32:1486-582
x Wilkins GT, Weyman AE, Abascal VM, Bloch PC, Palacios IF Percutaneous balloon dilatation of the mitral valve: an analysis of echocardiographic variables related to outcome and the
mechanism of dilatation Br Heart J 1998;60:299-308
x Wigle ED, Rakowski H, Kimball BP, Williams WG Hypertrophic
cardiomyopathy: clinical spectrum and treatment Circulation 1995;
92:1680-92
x Nagueh SF, Ommen SR, Lakkis NM, Killip D, Zoghbi WA, Schaff
HV, et al Comparison of ethanol septal reduction therapy with surgical myectomy for the treatment of hypertrophic obstructive
cardiomyopathy J Am Coll Cardiol 2001;38:1701-6
x Braun MU, Fassbender D, Schoen SP, Haass M, Schraeder R, Scholtz W, et al Transcatheter closure of patent foramen ovale in
patients with cerebral ischaemia J Am Coll Cardiol 2002;39:
2019-25
x Waight DJ, Cao Q-L, Hijazi ZM Interventional cardiac catheterisation in adults with congenital heart disease In: Grech
ED, Ramsdale DR, eds Practical interventional cardiology 2nd ed.
London: Martin Dunitz, 2002:390-406
ABC of Interventional Cardiology
Trang 3Julian Gunn, Ever D Grech, David Crossman, David Cumberland
Percutaneous coronary intervention has become a more
common procedure than coronary artery bypass surgery in
many countries, and the number of procedures continues to
rise In one day an interventionist may treat four to six patients
with complex, multivessel disease or acute coronary syndromes
Various balloons, stents, and other devices are delivered by
means of a 2 mm diameter catheter introduced via a peripheral
artery The success rate is over 95%, and the risk of serious
complications is low After a few hours patients can be
mobilised, and they are usually discharged the same or the next
day Even the spectre of restenosis is now fading
Refinements of existing techniques
The present success of percutaneous procedures is largely
because of refinement of our “basic tools” (intracoronary
guidewires and low profile balloons), which have greatly
contributed to the safety and effectiveness of procedures
However, the greatest technological advance has been in the
development of stents These are usually cut by laser from
stainless steel tubes into a variety of designs, each with different
radial strength and flexibility They are chemically etched or
electropolished to a fine finish and sometimes coated
Digital angiography is a great advance over cine-based
systems, and relatively benign contrast media have replaced the
toxic media used in early angioplasty Although magnetic
resonance and computed tomographic imaging may become
useful in the non-invasive diagnosis of coronary artery disease,
angiography will remain indispensable to guide percutaneous
interventions for the foreseeable future
New device technology
Pre-eminent among new devices is the drug eluting (coated)
stent, which acts as a drug delivery device to reduce restenosis
The first of these was the sirolimus coated Cypher stent
Triple vessel disease is no longer a surgical preserve, and particularly good results are expected with drug eluting stents In this case, lesions in the left anterior descending (LAD), circumflex (Cx), and right coronary arteries (RCA) (top row) are treated easily and rapidly by stent (S) implantation (bottom row)
Performance of percutaneous coronary intervention General statistics
x Success rate of procedure > 95%
x Symptoms improved after procedure 90%
x Restenosis 15% (range 5-50%)
x Duration of procedure 15 minutes-3 hours
x Access point:
Radial or brachial artery 5%
x Time in hospital after procedure:
x Intravenous contrast load 100-800 ml
x X ray dose to patient 75 Gy/cm 2
†
Special conditions
x Success of direct procedure for acute myocardial infarction > 95%
x Success for chronic ( > 3 month) occluded vessel 50-75%
x Mortality for procedure in severe cardiogenic shock 50%
x Restenosis:
Vessels < 2.5 mm in diameter, > 40 mm length 60% Vessels > 3.5 mm diameter, < 10 mm length 5%
x Lesion recurrence later than 6 months after procedure < 5%
x Re-restenosis:
After repeat balloon dilatation 30-50% After brachytherapy < 15%
*Death, myocardial infarction, coronary artery bypass surgery, cerebrovascular accident
†Equivalent to 1-2 computed tomography scans
Interventional devices and their uses
Stent 70-90% Most types
Drug eluting stent 0-50% High risk of restenosis
(possibly all) Cutting balloon 1-5% In-stent restenosis, ostial
lesions Rotablator 1-3% Calcified, ostial, undilatable
lesions Brachytherapy 1-3% In-stent restenosis
Atherectomy < 1% Bulky, eccentric, ostial lesions
Stent graft < 1% Aneurysm, arteriovenous
malformation, perforation Thrombectomy < 1% Visible thrombus
Laser < 1% Occlusions, in-stent restenosis
Distal protection < 1% Degenerate vein graft
Trang 4Sirolimus is one of several agents that have powerful antimitotic
effects and inhibit new tissue growth inside the artery and stent
In a randomised controlled trial (RAVEL) this stent gave a six
month restenosis rate of 0% compared with 27% for an
uncoated stent of the same design A later randomised study
(SIRIUS) of more complex stenoses (which are more prone to
recur) still produced a low rate of restenosis within stented
segments (9% v 36% with uncoated stents), even in patients with
diabetes (18% v 51% respectively) Other randomised studies
such as ASPECT and TAXUS II have also shown that coated
stents (with the cytotoxic agent paclitaxel) have significantly
lower six month restenosis rates than identical uncoated stents
(14% v 39% and 6% v 20% respectively) By reducing the
incidence of restenosis (and therefore recurrent symptoms),
drug eluting stents will probably alter the balance of treating
coronary artery disease in favour of percutaneous intervention
rather than coronary artery bypass surgery However, coated
stents will not make any difference to the potential for
percutaneous coronary intervention to achieve acute success in
any given lesion; nor do they seem to have any impact on acute
and subacute safety
Although coated stents may, paradoxically, be too effective at
altering the cellular response and thus delay the desirable
process of re-endothelialisation, there is no evidence that this is
a clinical problem However, this problem has been observed
with brachytherapy (catheter delivered radiotherapy over a
short distance to kill dividing cells), a procedure that is generally
reserved for cases of in-stent restenosis This may lead to late
thrombosis as platelets readily adhere to the “raw” surface that
results from an impaired healing response This risk is
minimised by prolonged treatment with antiplatelet drugs and
avoiding implanting any fresh stents at the time of
brachytherapy
Other energy sources may also prove useful Sonotherapy
(ultrasound) may have potential, less as a treatment in its own
right than as a facilitator for gene delivery, and is “benign” in its
effect on healthy tissue Photodynamic therapy (the interaction
of photosensitising drug, light, and tissue oxygen) is also being
investigated but is still in early development Laser energy, when
delivered via a fine intracoronary wire, is used in a few centres
to recanalise blocked arteries
New work practices
Twenty years ago, a typical angioplasty treated one proximally
located lesion in a single vessel in a patient with good left
ventricular function Now, it commonly treats two or three vessel
disease, perhaps with multiple lesions (some of which may be
complex), in patients with impaired left ventricular function,
advanced age, and comorbidity Patients may have undergone
Names of trials
x ASPECT—Asian paclitaxel-eluting stent clinical trial
x RAVEL—Randomized study with the sirolimus eluting velocity balloon expandable stent in the treatment of patients with de novo native coronary artery lesions
x SIRIUS—Sirolimus-coated velocity stent in treatment of patients with de novo coronary artery lesions trial
x TAXUS II—Study of the safety and superior performance of the TAXUS drug-eluting stent versus the uncoated stent on de novo lesions
Angiograms showing severe, diffuse, in-stent restenosis in the left anterior descending artery and its diagonal branch (L and D, left) This was treated with balloon dilatation and brachytherapy with irradiation (Novoste) from
a catheter (Br, centre), with an excellent final result (right)
Angiogram of an aortocoronary vein graft with an aneurysm and stenoses (A and S, top) Treatment by implantation of a membrane-covered stent excluded the aneurysm and restored a tubular lumen (bottom)
Bifurcation lesions, such as of the left anterior descending artery and its diagonal branch (L and D, left), are technically challenging to treat but can be well dilated by balloon dilatation and selective stenting (S, right)
Unprotected left main stem stenoses (LMS, top) may, with careful selection,
be treated by stent implantation (S, bottom).
Best results (similar to coronary artery bypass surgery) are achieved in stable patients with good left ventricular function and no other disease.
Close follow up to detect restenosis is important.
descending artery, Cx=
circumflex coronary artery)
ABC of Interventional Cardiology
Trang 5coronary artery bypass surgery and be unsuitable for further
heart surgery Isolated left main stem and ostial right coronary
artery lesions, though requiring more experience and
variations on traditional techniques, are also no longer a
surgical preserve
Role of percutaneous coronary intervention
The role of percutaneous intervention has extended to the
point where up to 70% of patients treated have acute coronary
syndromes Trial data now support the use of a combination of
a glycoprotein IIb/IIIa inhibitor and early percutaneous
intervention to give high risk patients the best long term results
The same applies to acute myocardial infarction, where
percutaneous procedures achieve a much higher rate of arterial
patency than thrombolytic treatment Even cardiogenic shock,
the most lethal of conditions, may be treated by an aggressive
combination of intra-aortic balloon pumping and percutaneous
intervention
The potential for percutaneous procedures to treat a wide
range of lesions successfully with low rates of restenosis raises
the question of the relative roles of percutaneous intervention
and bypass surgery in everyday practice It takes time to
accumulate sufficient trial data to make long term
generalisations possible
Early trials comparing balloon angioplasty with bypass
surgery rarely included stents and few patients with three vessel
disease (as such disease carried higher risk and percutaneous
intervention was not as widely practised as now) The long term
results favoured bypass surgery, but theses trials are now
outdated In the second generation of studies, stents were used
in percutaneous intervention, improving the results As in the
early studies, surgery and intervention had similarly low
complications and mortality The intervention patients still had
more need for repeat procedures because of restenosis than the
bypass surgery patients, but the differences were less
The major drawback of all these studies was an exclusion
rate approaching 95%, making the general clinical application
of the findings questionable This was because it was unusual at
that time to find patients with multivessel disease who were
technically suitable for both methods and thus eligible for
inclusion in the trials Now that drug eluting stents are available,
more trials are under way: the balance will now probably tip in
favour of percutaneous coronary intervention Meanwhile, the
decision of which treatment is better for a patient at a given
time is based on several factors, including the feasibility of
percutaneous intervention (which is generally considered as the
first option), completeness of revascularisation, comorbidity,
age, and the patient’s own preferences
Implications for health services
These issues are likely to pose major problems for health
services Modern percutaneous techniques can be used both to
shorten patients’ stay in hospital and to make their treatment
minimally hazardous and more comfortable They can also be
used in the first and the last (after coronary artery bypass
surgery) stages of a patient’s “ischaemic career.”
On the other hand, for the role of percutaneous coronary
intervention in acute infarction to be realised, universal
emergency access to this service will be needed However, most
health systems cannot afford this—the main limiting factor
being the number of interventionists and supporting staff
required to allow a 24 hour rota compatible with legal working
hours and the survival of routine elective work
An acute coronary syndrome was found to be due to stenoses and an ulcerated plaque in the right coronary artery (S and U, left) This was treated with a glycoprotein IIb/IIIa inhibitor followed by stent implantation (right) This is an increasingly common presentation of coronary artery disease to catheterisation laboratories
Right coronary artery containing large, lobulated thrombus (T, left) on a substantial stenosis After treatment with glycoprotein IIb/IIIa inhibitor, the lesion was stented successfully (St, right)
General roles of percutaneous coronary intervention (PCI) and coronary artery bypass surgery (CABG)
Condition
PCI
CABG
Acute presentation
Acute coronary syndrome ++ +++ ++ Cardiogenic shock +/ − + +/ − Acute full thickness myocardial infarction + +++ − Bailout after failed thrombolysis + ++ −
Chronic presentation
Impaired left ventricle with left main stem stenosis and blocked right coronary artery
− − − +++ Impaired left ventricle and 3 vessel disease + ++ +++ Impaired left ventricle and 3 vessel disease
with >1 occlusion − + +++ Diabetes and 3 vessel disease + ++ +++ Good left ventricle and 3 vessel disease + ++ +++
2 occluded vessels − − ++ Good left ventricle and 2 vessel disease + +++ ++ Repeat revascularisation after PCI ++ +++ ++ Good left ventricle and 1 vessel disease +++ +++ + 2-3 vessel diffuse or distal disease + ++ + Repeat revascularisation after CABG + ++ + Palliative partial revascularisation + ++ − Revascularisation of frail patient or with
severe comorbidity
+ ++ −
+++ highly effective role, ++ useful role, + limited role, − treatment not preferred, − − treatment usually strongly advised against
Trang 6The future for percutaneous coronary
intervention
Will percutaneous coronary intervention exist in 20 years time,
or, at least, be recognisable as a logical development of today’s
procedures? Will balloons and stents still be in use? It is likely
that percutaneous procedures will expand further, although
some form of biodegradable stent is a possibility A more
“biological” stent might also be able to act as an effective drug
or gene reservoir, which may extend local drug delivery into
new areas of coronary artery disease We may find ourselves
detecting inflamed (“hot”) plaques with thermography catheters
and treating these before they rupture We may even be able to
modify the natural course of coronary artery disease by
releasing agents “remotely” (possibly using an external
ultrasound trigger) or by injecting an agent that activates the
molecular cargo in a stent
A persistent challenge still limiting the use of percutaneous
coronary intervention is that of chronic total occlusions, which
can be too tough to allow passage of an angioplasty guidewire
An intriguing technique is percutaneous in situ coronary artery
bypass With skill and ingenuity, a few enthusiasts have
anastomosed the stump of a blocked coronary artery to the
adjacent cardiac vein under intracoronary ultrasound guidance,
thereby using the vein as an endogenous conduit (with reversed
flow) This technique may assist only a minority of patients
More practical, we believe, is the concept of drilling through
occlusions with some form of external guidance, perhaps
magnetic fields
“Direct” myocardial revascularisation (punching an array of
holes into ischaemic myocardium) has had a mixed press over
the past decade Some attribute its effect to new vessel
formation, others cite a placebo effect Although the channels
do not stay open, they seem to stimulate new microvessels to
grow Injection of growth factors (vascular endothelial growth
factor and fibroblast growth factor) to induce new blood vessel
growth also has this effect, and percutaneous injection of these
agents into scarred or ischaemic myocardium is achievable
However, we need a more thorough understanding of
biological control mechanisms before we can be confident of
the benefits of this technology
Challenges to mechanical revascularisation
Deaths from coronary artery disease are being steadily reduced
in the Western world However, with increasing longevity, it is
unlikely that we will see a reduction in the prevalence of its
chronic symptoms More effective primary and secondary
prevention; antismoking and healthy lifestyle campaigns; and
the widespread use of antiplatelet drugs, blockers, statins, and
renin-angiotensin system inhibitors may help prevent, or at
least delay, the presentation of symptomatic coronary artery
disease In patients undergoing revascularisation, they are
essential components of the treatment “package.” More effective
anti-atherogenic treatments will no doubt emerge in the near
future to complement and challenge the dramatic progress
being made in percutaneous coronary intervention
Further reading
x Morice M-C, Serruys PW, Sousa JE, Fajadet J, Ban Hayashi E, Perin
M, et al A randomized comparison of a sirolimus-eluting stent with
a standard stent for coronary revascularization N Engl J Med
2002;346:1773-80
x Park SJ, Shim WH, Ho DS, Raizner AE, Park SW, Hong MK, et al.
A paclitaxel-eluting stent for the prevention of coronary restenosis.
N Engl J Med 2003;348:1537-45
x Raco DL, Yusuf S Overview of randomised trials of percutaneous coronary intervention: comparison with medical and surgical therapy for chronic coronary artery disease In: Grech ED,
Ramsdale DR, eds Practical interventional cardiology 2nd ed.
London: Martin Dunitz, 2002:263-77
x Teirstein PS, Kuntz RE New frontiers in interventional cardiology:
intravascular radiation to prevent restenosis Circulation 2001;104:
2620-6
x Tsuji T, Tamai H, Igaki K, Kyo E, Kosuga K, Hata T, et al.
Biodegradable stents as a platform to drug loading Int J Cardiovasc
Intervent 2003;5:13-6
x Hariawala MD, Sellke FW Angiogenesis and the heart: therapeutic
implications J R Soc Med 1997;90:307-11
x Serruys PW, Unger F, Sousa JE, Jatene A, Bonnier HJ, Schonberger
JP, et al, for the Arterial Revascularization Therapies Study Group Comparison of coronary-artery bypass surgery and stenting for the
treatment of multivessel disease N Engl J Med 2001;344:1117-24
x SoS Investigators Coronary artery bypass surgery versus percutaneous coronary intervention with stent implantation in patients with multivessel coronary artery disease (the stent or
surgery trial): a randomised controlled trial Lancet 2002;360:
965-70
The coronary artery imaging was provided by John Bowles, clinical specialist radiographer, and Nancy Alford, clinical photographer, Sheffield Teaching Hospitals NHS Trust, Sheffield.
Competing interests: None declared.
ABC of Interventional Cardiology
Trang 7Gerry C Kaye
Before the 1980s, cardiac electrophysiology was primarily used
to confirm mechanisms of arrhythmia, with management
mainly by pharmacological means However, recognised
shortcomings in antiarrhythmic drugs spurred the development
of non-pharmacological treatments, particularly radiofrequency
ablation and implantable defibrillators
The two major mechanisms by which arrhythmias occur are
automaticity and re-entrant excitation Most arrhythmias are of
the re-entrant type and require two or more pathways that are
anatomically or functionally distinct but in electrical contact
The conduction in one pathway must also be slowed to a
sufficient degree to allow recovery of the other so that an
electrical impulse may then re-enter the area of slowed
conduction
Intracardiac electrophysiological
studies
Intracardiac electrophysiological studies give valuable
information about normal and abnormal electrophysiology of
intracardiac structures They are used to confirm the
mechanism of an arrhythmia, to delineate its anatomical
substrate, and to ablate it The electrical stability of the ventricles
can also be assessed, as can the effects of an antiarrhythmic
regimen
Atrioventricular conduction
Electrodes positioned at various sites in the heart can give only
limited data about intracardiac conduction during sinus rhythm
at rest “Stressing” the system allows more information to be
generated, particularly concerning atrioventricular nodal
conduction and the presence of accessory pathways
By convention, the atria are paced at 100 beats/min for
eight beats The ninth beat is premature (extrastimulus), and the
AH interval (the time between the atrial signal (A) and the His
signal (H), which represents atrioventricular node conduction
Tachyarrhythmias
Ischaemic Non-ischaemic
Junctional re-entry tachycardia Atrioventricular
re-entry tachycardia Atrial
ectopy Atrial
fibrillation Atrial
flutter Supraventricular tachycardias Ventricular tachycardias
Concealed accessory pathways
Overt accessory pathways (such as Wolff-Parkinson-White syndrome)
Classification of arrhythmias
Indications for electrophysiological studies Investigation of symptoms
x History of persistent palpitations
x Recurrent syncope
x Presyncope with impaired left ventricular function
Interventions
x Radiofrequency ablation—Accessory pathways, junctional tachycardias, atrial flutter, atrial fibrillation
x Investigation of arrhythmias (narrow and broad complex) with or without radiofrequency ablation
x Assessment or ablation of ventricular arrhythmias
Contraindications
x Severe aortic stenosis, unstable coronary disease, left main stem stenosis, substantial electrolyte disturbance
CSE
CSE
Tricuspid valve
Tricuspid valve
Coronary sinus ostium
Mitral valve
Diagrams showing position of pacing or recording electrodes in the heart in the right anterior oblique and left anterior oblique views (views from the right and left sides of the chest respectively) HRA=high right atrial electrode, usually on the lateral wall or appendage; HBE=His bundle electrode, on the medial aspect of the tricuspid valve; RVA=right ventricular apex; CSE=coronary sinus electrode, which records electrical deflections from the left side of the heart between the atrium and ventricle
A B A
B
Normal
sinus
rhythm
Initiation by premature extrasystole (or extrastimulus) causing unidirectional block due
to longer refractory period down one arm
Tachycardia due
to re-entry continues
Area of slow
conduction
A B
Mechanism of a re-entry circuit An excitation wave is propagated at a
normal rate down path A, but slowly down path B An excitation wave from
an extrasystole now encounters the slow pathway (B), which is still
refractory, creating unidirectional block There is now retrograde
conduction from path A, which coincides with the end of the refractory
period in path B This gives rise to a persistent circus movement
Trang 8time) is measured This sequence is repeated with the ninth beat
made increasingly premature In normal atrioventricular nodal
conduction, the AH interval gradually increases as the
extrastimulus becomes more premature and is graphically
represented as the atrioventricular nodal curve The gradual
prolongation of the AH interval (decremental conduction) is a
feature that rarely occurs in accessory pathway conduction
Retrograde ventriculoatrial conduction
Retrograde conduction through the atrioventricular node is
assessed by pacing the ventricle and observing conduction back
into the atria The coronary sinus electrode is critically
important for this It lies between the left ventricle and atrium
and provides information about signals passing over the left
side of the heart The sequence of signals that pass from the
ventricle to the atria is called the retrograde activation
sequence
If an accessory pathway is present, this sequence changes:
with left sided pathways, there is an apparent “short circuit” in
the coronary sinus with a shorter ventriculoatrial conduction
time This is termed a concealed pathway, as its effect cannot be
seen on a surface electrocardiogram It conducts retrogradely
only, unlike in Wolff-Parkinson-White syndrome, where the
pathway is bidirectional Often intracardiac electrophysiological
studies are the only way to diagnose concealed accessory
pathways, which form the basis for many tachycardias with
narrow QRS complexes
Supraventricular tachycardia
Supraventricular tachycardias have narrow QRS complexes
with rates between 150-250 beats/min The two common
mechanisms involve re-entry due to either an accessory
pathway (overt as in Wolff-Parkinson-White syndrome or
concealed) or junctional re-entry tachycardia
Accessory pathways
These lie between the atria and ventricles in the atrioventricular
ring, and most are left sided Arrhythmias are usually initiated
by an extrasystole or, during intracardiac electrophysiological
studies, by an extrastimulus, either atrial or ventricular The
extrasystole produces delay within the atrioventricular node,
allowing the signal, which has passed to the ventricle, to re-enter
the atria via the accessory pathway This may reach the
atrioventricular node before the next sinus beat arrives but
when the atrioventricular node is no longer refractory, thus
allowing the impulse to pass down the His bundle and back up
to the atrium through the pathway As ventricular
depolarisation is normal, QRS complexes are narrow This
circuit accounts for over 90% of supraventricular tachycardias in
HBE1-2 V5
CS1-2
CS3-4
CS5-6
CS7-8
CS9-10
HRA3-4
HBE1-2 V5
CS1-2
CS3-4
CS5-6
CS7-8
CS9-10
HRA3-4
A
A
A
A
A
A
A
A
A A
A
A
VP
VP VP
V
V V V V V
V
V V
V
V
Coronary sinus electrode signals, with poles CS9-10 placed proximally near the origin of the coronary sinus and poles 1-2 placed distally reflecting changes in the left ventricular-left atrial free wall Top: normal retrograde activation sequence with depolarisation passing from the ventricle back through the atrioventricular node to the right atrium and simultaneously across the coronary sinus to the left atrium Bottom: retrograde activation sequence in the presence of an accessory pathway in the free wall of the left ventricle showing a shorter ventriculoatrial (VA) time than would be expected in the distal coronary sinus electrodes (CS1-2) Such a pathway would not be discernible from a surface electrocardiogram
Mechanisms for orthodromic (left) and antedromic (right) atrioventricular re-entrant tachycardia
A1A2 (msec)
H1
H2
0 100 200 300 400 500 600 700
0
200
300
400
500
600
700
100
A normal atrioventricular nodal
“hockey stick” curve during antegrade conduction of atrial extrastimuli As the atrial extrastimulus (A 1 -A 2 ) becomes more premature, the AH interval (H 1 -H 2 ) shortens until the atrioventricular node becomes functionally refractory
ABC of Interventional Cardiology
Trang 9Wolff-Parkinson-White syndrome Rarely, the circuit is reversed,
and the QRS complexes are broad as the ventricles are fully
pre-excited This rhythm is often misdiagnosed as ventricular in
origin
Treatment—Pathway ablation effects a complete cure by
destroying the arrhythmia substrate Steerable ablation
catheters allow most areas within the heart to be reached The
left atrium can be accessed either retrogradely via the aortic
valve, by flexing the catheter tip through the mitral valve, or
transeptally across the atrial septum Radiofrequency energy is
delivered to the atrial insertion of a pathway and usually results
in either a rapid disappearance of pre-excitation on the surface
electrocardiogram or, in the case of concealed pathways,
normalisation of the retrograde activation sequence Accessory
pathway ablation is 95% successful Failure occurs from an
inability to accurately map pathways or difficulty in delivering
enough energy, usually because of positional instability of the
catheter Complications are rare ( < 0.5%) and are related to
vascular access—femoral artery aneurysms or, with left sided
pathways, embolic cerebrovascular accidents
Junctional re-entry tachycardia
This is the commonest cause of paroxysmal supraventricular
tachycardia The atrioventricular nodal curve shows a sudden
unexpected prolongation of the AH interval known as a “jump”
in the interval The tachycardia is initiated at or shortly after the
jump The jump occurs because of the presence of two
pathways—one slowly conducting but with relatively rapid
recovery (the slow pathway), the other rapidly conducting but
with relatively slow recovery (the fast pathway)—called duality of
atrioventricular nodal conduction This disparity between
conduction speed and recovery allows re-entrance to occur On
a surface electrocardiogram the QRS complexes are narrow,
and the P waves are often absent or distort the terminal portion
of the QRS complex These arrhythmias can often be
terminated by critically timed atrial or ventricular extrastimuli
In the common type of junctional re-entry tachycardia (type
A) the circuit comprises antegrade depolarisation of the slow
pathway and retrograde depolarisation of the fast pathway
Rarely ( < 5% of junctional re-entry tachycardias) the circuit is
reversed (type B) The slow and fast pathways are anatomically
separate, with both inputting to an area called the compact
atrioventricular node The arrhythmia can be cured by mapping
and ablating either the slow or fast pathway, and overall success
occurs in 98% of cases Irreversible complete heart block
requiring a permanent pacemaker occurs in 1-2% of cases, with
the risk being higher for fast pathway ablation Therefore, slow
pathway ablation is the more usual approach
Atrial flutter and atrial fibrillation
Atrial flutter is a macro re-entrant circuit within the right
atrium The critical area of slow conduction lies at the base of
the right atrium in the region of the slow atrioventricular nodal
pathway Producing a discrete line of ablation between the
tricuspid annulus and the inferior vena cava gives a line of
electrical block and is associated with a high success rate in
terminating flutter Flutter responds poorly to standard
antiarrhythmic drugs, and ablation carries a sufficiently
impressive success rate to make it a standard treatment
Atrial fibrillation is caused by micro re-entrant wavelets
circulating around the great venous structures, or it may be
related to a focus of atrial ectopy arising within the pulmonary
veins at their junction with the left atrium The first indication
that atrial fibrillation was electrically treatable came from the
Maze operation (1990) Electrical dissociation of the atria from
the great veins was carried out by surgical excision of the veins
V1 1
CS DIST 1
CS PROX 1
ABL CATH 2.5
V5 1
Surface electrocardiogram leads V1 and V5 and signals from the distal coronary sinus electrodes (CS dist), proximal electrodes (CS prox), and the tip of the ablation catheter (ABL CATH) during pathway ablation to treat Wolff-Parkinson-White syndrome The onset of radiofrequency energy (thin arrow) produces loss of pre-excitation after two beats with a narrow complex QRS seen at the fourth beat (broad arrow) Prolongation of the AV signal in the coronary sinus occurs when pre-excitation is lost
A1A2 (msec)
0 100 200 300 400 500 600 700 0
200 300 400 500 600 700
100
A1A2 (msec)
0 100 200 300 400 500 600 700
Atrioventricular nodal curves In a patient with slow-fast junctional re-entrant tachycardia (left) there is a “jump” in atrioventricular nodal conduction when conduction changes from the fast to the slow pathway In a patient with accessory pathways conducting antegradely (such as
Wolff-Parkinson-White syndrome) there is no slowing of conduction as seen
in the normal atrioventricular node, and the curve reflects conduction exclusively over the pathway (right)
Slow pathway
Fast pathway
Slow pathway
Fast pathway Circus
motion
Atrial beat premature
Mechanism of slow-fast junctional re-entrant tachycardia A premature atrial impulse finds the fast pathway refractory, allowing retrograde conduction back up to the atria
Trang 10from their insertion sites and then suturing them back The
scarred areas acted as insulation, preventing atrial wave-fronts
from circulating within the atria Similar lines of block can be
achieved by catheter ablation within the right and left atria The
results look promising, although this is a difficult, prolonged
procedure with a high relapse rate Of more interest is a
sub-group of patients with runs of atrial ectopy, which
degenerate to paroxysms of atrial fibrillation These
extrasystoles usually originate from the pulmonary veins, and
their ablation substantially reduces the frequency of
symptomatic atrial fibrillation With better understanding of the
underlying mechanisms and improved techniques, atrial
fibrillation may soon become a completely ablatable
arrhythmia
Ventricular tachycardia
Ventricular tachycardia carries a serious adverse prognosis,
particularly in the presence of coronary artery disease and
impaired ventricular function Treatment options include drugs,
occasional surgical intervention (bypass or arrhythmia surgery),
and implantable defibrillators, either alone or in combination
Ventricular tachycardia can be broadly divided into two groups,
ischaemic and non-ischaemic The latter includes arrhythmias
arising from the right ventricular outflow tract and those
associated with cardiomyopathies
Since the radiofrequency energy of an ablation catheter is
destructive only at the site of the catheter tip, this approach
lends itself more to arrhythmias where a discrete abnormality
can be described, such as non-ischaemic ventricular tachycardia
In ischaemic ventricular tachycardia, where the abnormal
substrate often occurs over a wide area, the success rate is lower
Ideally, the arrhythmia should be haemodynamically stable,
reliably initiated with ventricular pacing, and mapped to a
localised area within the ventricle In many cases, however, this
is not possible The arrhythmia may be unstable after initiation
and therefore cannot be mapped accurately The circuit may
also lie deep within the ventricular wall and cannot be fully
ablated However, detailed intracardiac maps can be made with
multipolar catheters A newer approach is the use of a
non{contact mapping catheter, which floats freely within the
ventricles but senses myocardial electrical circuits
Although the overall, long term, success rate for
radiofrequency ablation of ischaemic ventricular tachycardia is
only about 65%, this may increase
Conclusion
The electrophysiological approach to treating arrhythmias has
been revolutionised by radiofrequency ablation Better
computerised mapping, improved catheters, and more efficient
energy delivery has enabled many arrhythmias to be treated
and cured The ability to ablate some forms of atrial fibrillation
and improvement in ablation of ventricular tachycardia is
heralding a new age of electrophysiology Ten years ago it could
have been said that electrophysiologists were a relatively benign
breed of cardiologists who did little harm but little good either
That has emphatically changed, and it can now be attested that
electrophysiologists exact the only true cure in cardiology
Diagram of basket-shaped mapping catheter with several recording electrodes (red dots) The basket retracts into a catheter for placement in either the atria or ventricles.
Once it is in position, retraction of the catheter allows the basket to expand
Further reading
x Olgin JE, Zipes DP Specific arrhythmias: diagnosis and treatment.
In: Braunwald E, Zipes DP, Libby P, eds Heart disease 6th ed.
Philadelphia: Saunders, 2001:1877-85
x McGuire MA, Janse MJ New insights on the anatomical location of components of the reentrant circuit and ablation therapy for
atrioventricular reentrant tachycardia Curr Opin Cardiol 1995;
10:3-8
x Jackman WM, Beckman KJ, McClelland JH, Wang X, Friday KJ, Roman CA, et al Treatment of supraventricular tachycardia due to atrioventricular nodal re-entry by radiofrequency catheter ablation
of the slow-pathway conduction N Engl J Med 1992;327:313-8
x Calkins H, Leon AR, Deam AG, Kalbfleisch SJ, Langberg JJ, Morady F Catheter ablation of atrial flutter using radiofrequency
energy Am J Cardiol 1994;73:353-6
x Schilling RJ, Peter NS, Davies DW Feasibility of a non-contact catheter for endocardial mapping of human ventricular
tachycardia Circulation 1999;99:2543-52
Competing interests: None declared.
The diagrams showing the mechanisms of orthodromic and antedromic atrioventricular re-entrant tachycardia and of slow-fast atrioventricular nodal re{entrant tachycardia are reproduced from ABC of Clinical
Electrocardiography, edited by Francis Morris, 2002.
ABC of Interventional Cardiology